Research has focused on the cloning and characterization of a gene that could be related to Waardenburg syndrome. We had previously analyzed the transgenic mouse, miVGA9, which has a similar phenotype and had found that a lack of melanocytes is responsible for the phenotype. The human homologue of the gene, whose mutations were found in the miVGA9 homologue and other microphthalmia mice, was cloned from a human melanocyte cDNA library. This gene, designated MITF (microphthalmia-associated transcription factor), encodes a transcription factor with the structure of basic-helix-loop-helix-zipper. This gene was assigned to chromosome 3p14.1-p12.3 by in situ hybridization. Diallelic restriction fragment length polymorphism was found with the restriction enzyme BbsI. These alleles showed codominant inheritance. MITF gene was further characterized by transfecting it into NIH3T3 cells. It was found that one of the functions of MITF is related to the differentiation of melanocytes.